Harnessing the power of the human foot
A device already on the market converts the energy of walking into electricity. The Pioneer shoe uses this current to power little headlights built into the toes, so those walking in the dark will have their way illuminated up to more than a yard ahead. A battery in the sole stores electricity so that the wearer does not experience pulsing of the LED beam.
The second idea is a great solution to the dead battery problem. The Weza Portable Energy Source from Freeplay allows the user to harness the power of his foot to build up enough of a charge to jump-start a car. Unlike the portable battery units that themselves require recharging from time to time, the Weza will work any time one can summons the energy to pump it up. Unfortunately, at $299 I doubt many will line up for one.
The third idea, more speculative at this point, is the Crowd Farm. This concept, developed by two MIT students, proposes flooring public places in materials that gather the energy of the pedestrian footsteps, converting it to electricity. They estimate the foot traffic in a busy transportation depot such as Victoria Station could power 6,500 LEDs. Details of the technology are still being worked out. As part of their research, the two built a stool that lights up using electricity generated by the weight of the person sitting upon it.
We expend a tremendous amount of energy with every step we take. These new technologies represent a huge step forward in leveraging our war against gravity.